The rising prevalence of obesity is taking an increasingly severe toll on the nation's health. Achieving and maintaining a medically significant weight loss is of particular importance for those overweight individuals who have, or who are at greatest risk for developing, one of the many medical conditions associated with obesity. The present proposal is aimed at evaluating three treatments for weight loss maintenance in primary care practices where such patients are routinely treated. One treatment consists of a conventional lifestyle change program (based on the LEARN manual). The second consists of the LEARN program plus the use of meal replacements (MRs) to facilitate weight loss maintenance. The third consists of LEARN+MR and a Reduced Energy Density Eating program (REDE). The three treatments will be administered using two different modes of delivering the programs, one group-based (where an outside expert leads a traditional weight control program) and the other practice-based (where physicians and a practice-based care manager collaborate to deliver the program to individual patients). Participants will consist of 312 overweight and obese primary care patients. All participants will initially lose weight on identical 1,200-1,500 kcal/day diets (consisting of two MRs and a healthy dinner), after which one of the three maintenance interventions will be introduced. A second aim of the study is to investigate the mechanisms responsible for differential weight maintenance outcomes. A final aim is to examine several individual difference measures as potential moderators of study outcomes, both alone and in combination with treatment condition. This study is important because it may identify better ways of promoting long-term improvements in diet and body weight in overweight patients seen in primary care settings. Participants will receive treatment during a one-year period and follow-up assessments will be conducted one and two years after treatment ends. Outcome will be assessed in terms of changes in body weight and composition, nutritional composition of the diet, measures of eating control, overeating, and quality of life, physical activity, patient and physician satisfaction ratings, cost-effectiveness, and several medical risk factors (blood pressure, lipids, fasting glucose, and HbAlc).